CN112292253B

CN112292253B - Additive manufacturing using thermotropic liquid crystalline polymers

Info

Publication number: CN112292253B
Application number: CN201980041754.2A
Authority: CN
Inventors: 西尔万·甘滕拜因; 库纳尔·马萨尼亚; 西奥·特沃特; 安德烈·斯图达特; 延斯·塞塞格; 威廉·沃伊格克
Original assignee: Eidgenoessische Technische Hochschule Zurich ETHZ
Current assignee: Eidgenoessische Technische Hochschule Zurich ETHZ
Priority date: 2018-06-22
Filing date: 2019-06-21
Publication date: 2023-04-04
Anticipated expiration: 2039-06-21
Also published as: EP3810400A1; WO2019243575A1; KR20210022638A; JP2021529685A; CN112292253A; US20210323219A1; JP7376936B2; US11858197B2

Abstract

Additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, wherein the object is formed by one or several individual solid filamentary units, the additive manufacturing method comprising the steps of: -discharging the polymer composition in the molten state from the nozzles of the print head, so as to impart an oriented flow to the polymer composition in the molten state discharged from the nozzles of the print head, and depositing said discharged polymer composition in the molten state along at least one predetermined path, preferably a horizontal path, and solidifying the thread unit or units thus formed to form a solid thread unit or units of the object to be manufactured; -optionally repeating the previous step until said target is formed; wherein the polymer composition comprises a thermotropic liquid crystalline polymer as a polymer component of the polymer composition, said solid filamentous unit being characterized by a minimum thickness of one or several filamentous units equal to or less than 0.2mm, preferably equal to or less than 0.15mm, and more preferably equal to or less than 0.10mm, and most preferably between 0.1mm and 0.01mm.

Description

Additive manufacturing using thermotropic liquid crystalline polymers

Technical Field

The present invention relates to additive manufacturing processes for manufacturing three-dimensional objects using thermotropic liquid crystalline polymers or compositions thereof, in particular Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF).

Background

Structural materials combining low weight with high mechanical properties are critical for the manufacture of fuel efficient vehicles, biomedical implants and energy harvesting structures. The increasing use of fibre reinforced polymers as lightweight composite materials in aircraft, automobiles and wind turbines is strongly dependent on the production of stiff and strong fibres that must be successfully combined with a polymer matrix. High stiffness and strength are typically achieved using inherently strong fibrous materials (e.g., quartz glass) or polymers with a high degree of molecular orientation (e.g., high performance polyethylene fibers, aramid fibers, or carbon fibers). The molecular orientation required to produce strong fibers is achieved by a spinning process, which typically involves flow orientation followed by drawing of the material by orders of magnitude. Lightweight composites are then obtained by infiltrating the pre-assembled fibers with a softer polymer matrix or blending loose fibers into the softer polymer matrix. While the resulting materials can exhibit very high strength and stiffness, the energy-and labor-intensive manufacturing processes, the difficulty of recycling, and the typical brittle fracture of prior art composites present major challenges today.

To overcome some of these challenges of intensive manufacturing and cumbersome recycling, methods have been developed to produce highly oriented single phase Polymer structures, such as solid state stretched polypropylene tapes or spun extruded (LCP) Liquid Crystal Polymer (lc) sheets. These tapes or sheets can then be assembled by hot pressing into 3D monolithic parts combining recyclability with improved mechanical properties. Unfortunately, objects produced using these methods are limited to simple geometries that exhibit enhanced mechanical properties in a single direction, such as plates, shells, and stacked sheets.

Polymer objects with much more complex geometries can now be produced using 3D printing techniques such as Fused Deposition Modeling (FDM). However, this freedom in design is usually at the expense of poor mechanical properties. In contrast to the spinning process, current FDM printers use polymers that are not easily molecularly oriented and crystallized to prevent the build up of residual stress and warping. Performance polymers such as Acrylonitrile Butadiene Styrene (ABS) and Polylactide (PLA) are therefore typical feedstock materials. Higher levels of crystallinity and mechanical properties can be achieved by printing with high performance Polyetheretherketone (PEEK) using a heated printing chamber. However, the low molecular orientation and poor line adhesion (line adhesion) significantly degrade the overall mechanical properties of the printed part compared to injection molded engineering materials. These problems have severely limited the applicability of 3D printed polymers as lightweight structures in severe load-bearing applications. In this case, a manufacturing route that harmonizes the forming freedom of 3D printing with high mechanical properties obtained by molecular orientation, improved filament adhesion, and high recyclability is not currently available.

Although Liquid Crystalline Polymers (LCP) are known (e.g. based on thermotropic polyesters, e.g. from

) Can be 3D printed into a fully recyclable, lightweight structure, but the mechanical properties of known 3D printed structures fall significantly short of what could theoretically be achieved.

Robert W.Gray,Donald G.Baird,Jan Helge

(1998) "Effects of processing conditions on short TLCP fiber reinforced FDM parts", rapid deposition Journal, vol.4, no. 1, pages 14-25 disclose a Fused Deposition Modeling (FDM) process using the Stratasys FDM 1600 system, wherein the material deposited is a chopped short fiber reinforced polypropylene matrix of Thermotropic Liquid Crystalline Polymer (TLCP) commercially available under the trademark VECTRA A A950. Likewise, a fused deposition modeling method for pure TLCP is disclosed, wherein plates (plats) are produced by depositing a melt of TLCP through a nozzle orifice having a diameter of 0.64 mm. While pure TLCP targets made in this manner are easy to recycle, the mechanical properties of pure TLCP sheets obtained by FDM are not as good as injection molded sheets or spun drawn TLCP filaments of pure TLCP.

EP0 668 379 A1 discloses a method of melt spinning a liquid crystal polymer arbitrarily onto a die to form a nonwoven web of liquid crystal polymer to obtain a shaped object.

US 9,186,848 B2 discloses such additive manufacturing: it uses a so-called "tow-prepreg" as the feed filament, heating the "tow-prepreg" so that the polymer composition of the continuous roving surrounding the solid core melts and wets the solid core and deposits the solid, heated "tow-prepreg" to form the target.

Thus, there is currently a need to provide an additive manufacturing method: wherein the mechanical properties of the object made of TLCP can be further improved when compared to the object made of the existing TLCP, while it can be recycled in a simple manner.

Disclosure of Invention

By the object manufactured by the additive manufacturing method according to the invention, a desired combination of recyclability and mechanical properties is obtained.

It is an object of the present invention to provide an additive manufacturing method of manufacturing an object in an additive manufacturing apparatus, wherein the object is formed by one or several individual solid thread-like units, the additive manufacturing method comprising the steps of: discharging the polymer composition in the molten state from the nozzles of the print head, thereby imparting a flow to the polymer composition in the molten state discharged, and depositing it along at least one predetermined path (which may be a horizontal path) such that one or several solid threadlike units of the object to be manufactured are formed, and in case the object is formed by several individual solid threadlike units, optionally repeating the previous step until the object is formed; wherein the polymer composition comprises a thermotropic liquid crystalline polymer as a polymer component of the polymer composition, characterized in that the minimum thickness of at least one solid filamentary unit is equal to or less than 0.2mm, preferably equal to or less than 0.15mm and more preferably equal to or less than 0.10mm. It is understood that the temperature at which the polymer composition in the molten state is discharged from the nozzle of the print head is the temperature at which the thermotropic liquid crystalline polymer comprised in said polymer composition is in the molten or molten liquid crystalline state. Without wishing to be bound by a particular theory, it is believed that imparting an oriented flow to the polymer composition in the molten state as it is discharged results in an orientation within the polymer component of the polymer composition at the molecular level, and that this orientation is substantially maintained when performing the additive manufacturing method according to the present invention.

It has surprisingly been found that the formed solid threadlike units as well as the objects produced by expansion have greatly improved mechanical properties when the polymer composition is extruded such that the minimum thickness of one or several formed threadlike units is equal to or less than 0.2mm. Since the physical properties of known thermotropic liquid crystalline polymers above the melting point, such as melt viscosity, heat capacity, and thermal conductivity, are similar, it is foreseeable that the above-described requirement for maximum minimum thickness may apply to the entire thermotropic liquid crystalline polymer melt. In the case of additive manufacturing, the use of filamentary units having the above-mentioned diameters may be considered an counterintuitive decision, since typically in 3D printing speed is an issue, and typically does not take into account the reduction of the amount of molten polymer composition deposited on each path by diameter reduction, since this further increases the time required to achieve the object to be manufactured. However, in the case of polymer compositions comprising thermotropic liquid crystalline polymers as the polymer component of the polymer composition, the improvement of the mechanical properties is much more important than the loss of production speed.

In a preferred embodiment of an additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, the polymer composition in molten state is further actively cooled to form a solid filamentous subunit, and is actively cooled to form a solid filamentous subunit, preferably by forced convection.

In a preferred embodiment of the additive manufacturing method for manufacturing a target in an additive manufacturing apparatus, the formed target is subsequently subjected to in-situ or ex-situ annealing of the 3D printer at less than 100 ℃, more preferably less than 50 ℃, most preferably less than 25 ℃ below the melting temperature of the thermotropic liquid crystalline polymer for up to 6 hours or from 2 hours to 6 hours, preferably up to 9 hours or from 6 hours to 9 hours, more preferably up to 12 hours or from 9 hours to 12 hours, more preferably up to 48 hours or from 12 hours to 48 hours, and most preferably up to 96 hours or from 12 hours to 96 hours. Annealing was found to improve adhesion between individual solid filamentous subunits or adjacent portions thereof, thereby providing such targets: which exhibits increased mechanical stiffness and strength in combination with the favorable energy absorbing zigzag pattern of fracture in the stress-strain curve rather than the broom-like pattern of fracture.

In a preferred embodiment of an additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, the polymer composition is discharged from a nozzle of a print head along a linear or non-linear path. When the polymer composition is discharged from the nozzles of the print head along such a path, biomimetic structures with significant mechanical properties can be simulated in a given setup.

In a preferred embodiment of the additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, the polymer composition discharged from the nozzle of the print head in a molten state is in a melt crystalline state, i.e. the thermotropic liquid crystalline polymer of the polymer composition is in a melt crystalline state. In the molten liquid crystalline state, the melt contains a liquid crystal phase, and if the temperature is raised above a certain threshold, the liquid crystal phase in the melt will become an isotropic liquid. The temperature range over which a given thermotropic liquid crystalline polymer assumes a melt crystalline state can be found in the literature or can be determined experimentally without undue burden.

In a preferred embodiment of the additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, the thermotropic liquid crystalline polymer is an aromatic polyester, preferably a polyester obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid. The use of thermotropic liquid crystalline polymers allows for easier recycling by melting. The thermotropic liquid crystalline polymer obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid exhibits good mechanical properties and is aligned in the extrusion direction.

In a preferred embodiment of the additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, the temperature of the polymer composition discharged from the nozzle of the print head in a molten state is not more than 100 ℃, preferably not more than 50 ℃, preferably not more than 25 ℃, preferably not more than 15 ℃, preferably not more than 10 ℃, and more preferably not more than 5 ℃ higher than the melting temperature of the thermotropic liquid crystalline polymer.

In a preferred embodiment of the additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, the orifice of the nozzle has a substantially circular orifice and a diameter of less than 0.64mm or 0.05mm to 0.635mm, and preferably a diameter of less than 0.4mm or 0.05mm to 0.4mm, and more preferably a diameter of less than 0.31mm or 0.05mm to 0.305mm, or a substantially rectangular orifice and a diameter of less than 0.64mm or 0.05mm to 0.635mm, and preferably a diameter of less than 0.4mm or 0.05mm to 0.4mm, and more preferably a diameter of less than 0.31mm or 0.05mm to 0.305 mm.

It is a further object of the present invention to provide an object obtained by an additive manufacturing method according to the above additive manufacturing method, wherein the object comprises or consists of at least one solid filamentary unit having a minimum thickness equal to or less than 0.2mm, preferably equal to or less than 0.15mm, and more preferably equal to or less than 0.10mm, and most preferably between 0.01mm and 0.10mm, and/or the object is preferably free of reinforcing fibers, such as glass fibers or carbon fibers or aramid fibers or high modulus polyolefins. It will be understood that the minimum thickness corresponds to the diameter in the case of a filamentary element having a circular cross-section. In the case of a filamentary element having an elliptical cross-section, the minimum thickness corresponds to the minor axis. In the case of a filamentary element having a rectangular cross-section, the minimum thickness corresponds to the width. In the case of a filamentary element having a square cross-section, the minimum thickness corresponds to the length of one side. In yet another preferred embodiment, the object obtained by the additive manufacturing method according to the additive manufacturing method described above comprises or consists of one or several solid filamentary units having a minimum thickness equal to or less than 0.2mm, preferably equal to or less than 0.15mm, and more preferably equal to or less than 1.0mm, and most preferably between 0.01mm and 0.10mm, wherein in at least one region of the object or in the object as a whole the one or several solid filamentary units are arranged substantially in parallel in a single direction. In this case, the target is said to be "unidirectional" in the region or as a whole.

In a preferred embodiment of the object obtained by the additive manufacturing method according to the additive manufacturing method described above, the object comprises or consists of at least one solid filamentary unit having a young's modulus of 15GPa or higher and up to 50GPa, preferably 25GPa or higher and up to 50GPa, more preferably 30GPa or higher and up to 50GPa. In another embodiment, the object comprises or consists of at least one region having a Young's modulus of 15GPa or more, preferably 20GPa or more, 25GPa or more and up to 35GPa.

In a preferred embodiment of the object obtained by the additive manufacturing method according to the additive manufacturing method described above, the object comprises or consists of at least one solid filamentous unit having a tensile strength of 200MPa or more and up to 1GPa, preferably 400MPa or more and up to 1GPa, more preferably up to 600MPa or more and up to 1GPa. In another embodiment, the object comprises or consists of at least one region having a tensile strength of 200MPa and up to 500MPa, preferably 300MPa and up to 500MPa.

It is a further object of the invention to provide an additive manufacturing apparatus comprising at least one supply of a polymer composition and configured to perform additive manufacturing according to the above, characterized in that the polymer composition comprises a thermotropic liquid crystalline polymer as a polymer component of the polymer composition.

In a preferred embodiment of the additive manufacturing device according to the invention, the polymer component of the polymer composition is a thermotropic liquid crystalline polymer obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid.

In a preferred embodiment of the additive manufacturing apparatus according to the invention, the polymer component of the polymer composition is under the trade name Celanese Corporation

A950 a commercially available thermotropic liquid crystalline polymer.

In a preferred embodiment of the additive manufacturing apparatus according to the invention, the additive manufacturing apparatus further comprises a build volume provided with a heating device capable of maintaining the target in the build envelope at a temperature corresponding to an annealing temperature of the thermotropic liquid crystalline polymer. Due to the zigzag fracture pattern in the stress-strain curve rather than a single stress peak with a broom-like failure mode as observed for the unannealed target, it was found that annealing provides targets exhibiting improved mechanical properties, such as enhanced modulus of toughness. By including a build-up space equipped with a heating device, the target can be annealed in situ without transferring the target to a separate annealing chamber.

Further embodiments of the invention are set forth in the dependent claims.

Drawings

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, which are for the purpose of illustrating the presently preferred embodiments of the invention, and not for the purpose of limiting the same. In the drawings, LCP refers to a liquid crystalline polymer commercially sold by Celanese Corporation under the trade name Vectra a950, which is a thermotropic liquid crystalline polyester.

Fig. 1 shows in a: a false color SEM image of a single tensile tested filament; in b, c are shown: polarized light microscope images of filament cross sections of different diameters in both vertical (b) and horizontal (c) filaments; shown in d are: x-ray diffraction patterns of filaments of different diameters; shown in e are: young's modulus (9632;) and tenacity (. Tangle-solidup.) of the vertically extruded filaments depending on the nozzle diameter; shown in f are: young's modulus (9632;) and tenacity (. Tangle-solidup.) of horizontally extruded filaments depending on layer height; in g are shown: young's modulus (9632;) and strength (a) depending on the extrusion temperature; shown in h are: tensile strength depending on the annealing time of the horizontal filaments (. Tangle-solidup.) and the vertical filaments (. Xxx).

Fig. 2 shows in a: young's modulus of the unidirectional printed part depending on the printed orientation, and strength (. DELTA.) of the 0.05mm sample for print heights of 0.05mm (. Gamma.;), 0.1mm (. Diamond-solid.), 0.15mm (. Diamond-solid.), and 0.2mm (. Tangle-solidup.); in b is shown: for the annealed (. Tangle-solidup.) and non-annealed (. Diamond-solid.), the flexural modulus dependent on the print orientation (. Gamma.,) and the strength dependent on the print orientation (. Gamma.,) were determined; in c is shown: young's modulus (9632;) and ultimate tensile strength (a) depending on the annealing time for the samples in the transverse print direction; shown in d are: representative tensile stress-strain curves for the annealed (dashed line) and unannealed (solid line) unidirectional longitudinal samples.

Fig. 3 shows in a: representative stress-strain curves for open pore tensile samples for isotropic (dash-dot line), unidirectional unannealed (solid line) and annealed (dashed line) and oriented unannealed (thin dashed line) and annealed (dash-dot line/dashed line) samples; in b is shown: open pore strain maps (circles) measured by digital image correlation prior to fracture; in c is shown: an impact resistant Bouligand-type structure with a twisted plywood arrangement of printed fibres; in d are shown: biomedical implants with local bearing enhancement, wherein the printed lines are designed to follow the main stress direction around the hole.

Fig. 4 shows in a: for samples printed from LCP (\9632;), PLA (\9679;), and PEEK (. Diamond-solid.), the Young's modulus of the unidirectionally printed parts, which depends on the print orientation; in b is shown: for samples printed from unannealed LCP (\9632;), annealed LCP (. Tangle-solidup.), PLA (\9679;) and PEEK (. Diamond-solid.), the strength of the unidirectional printed part, depending on the printed orientation; in c is shown: a Hermans orientation factor as a function of nozzle diameter for perpendicularly printed filaments; shown in d are: hermans orientation factor as a function of layer height for horizontally printed filaments.

Fig. 5 shows in a: effect of layer height on Young's modulus for samples 0 ° (\9632;) and 90 ° (\9679;) and on strength for samples 0 ° (. Solidup.) and 90 ° (. Diamond-solid.); in b is shown: temperature dependence of Young's modulus for the 0 ° (\9632;) and 90 ° (\9679;) samples, and temperature dependence of strength for the 0 ° (. Tangle-solidup) and 90 ° (. Diamond-solid.) samples; in c is shown: representative curves of shear stress measurements for the unannealed (solid line) and annealed (dashed line) printed samples; shown in d are: young's modulus depending on annealing time for 0 ° uniaxially stretched sample; shown in e are: ultimate tensile strength of the unidirectional printed parts depending on the print orientation for samples with print heights of 0.05mm (\9632;), 0.1mm (\9679;), 0.15mm (. Diamond-solid.), and 0.2mm (. Tangle-solidup.); shown in f are: melt flow index of the virgin LCP particles, printed samples, and annealed printed samples.

Detailed Description

It is an object of the present invention to provide an additive manufacturing method for manufacturing an object in an additive manufacturing apparatus according to the subject matter of the claims.

Additive manufacturing (also known as 3D printing) involves manufacturing an object by depositing constituent materials of the object to be manufactured in a layer-by-layer manner. Techniques that may be used to deposit the constituent materials of the object to be fabricated in a layer-by-layer manner include material extrusion, binder jetting, material jetting, and directed energy deposition. Extrusion techniques are of particular interest in the context of the present invention. Additive manufacturing techniques that employ extrusion to deposit the constituent materials of the object to be fabricated, of particular interest for the purposes of the present invention, are fuse fabrication (FFF) or Fused Deposition Modeling (FDM) because the materials used for fabrication are conveniently available as filament spools or solid subunits of polymer, which are fed to a printhead where the material (typically a polymer composition) melts prior to discharge through nozzles of the printhead according to a predetermined path to form layers that make up the entire object in accordance with the fabricated object. It should be understood that in the context of the present invention, the number of print heads and/or the number of nozzles per print head is not particularly limited. Although manufacturing objects according to the present invention on a laboratory scale is typically done with additive manufacturing apparatus having a print head with a single nozzle, it is clear that on a larger scale a single additive manufacturing apparatus may be equipped with a plurality of print heads each having one or more nozzles working in unison to speed up the manufacturing of a single object or to produce multiple objects in parallel.

In an additive manufacturing method according to the invention for manufacturing an object in an additive manufacturing apparatus, the object is formed by one or several individual solid thread-like units or wires deposited in a layer-by-layer manner by nozzles of a print head in the additive manufacturing apparatus. For example, a first layer is printed, then the nozzle is raised and printing of the next layer is started, and so on until the target is formed. Alternatively, the support platform on which the first layer is printed is lowered and the nozzles begin printing the next layer.

The print head discharges the polymer composition in the molten state through a nozzle equipped with heating means capable of heating the polymer composition to a flowable state, i.e. a state in which the polymer components of the polymer composition (in particular, the thermotropic liquid crystalline polymer) are in the molten state or in the molten liquid crystalline state.

The polymer composition is discharged and deposited in the molten state along at least one predetermined path to form one or several solid thread-like units of the object to be manufactured. The one or several solid filamentary units may have different cross-sectional shapes, such as substantially circular, oval, rectangular or square.

In some cases, the object to be manufactured can be manufactured without interrupting the discharge of the polymer composition in the molten state. In other cases, the discharge of the polymer composition in the molten state can be interrupted between the layers or within the layers. However, when comparing the case where the object is formed of a single continuous solid thread unit with the case where the object is formed of several separate solid thread units, the mechanical properties are not significantly affected.

The polymer composition comprises a thermotropic liquid crystalline polymer as a polymer component of the polymer composition. It is to be understood that the polymer composition may thus essentially comprise a single thermotropic liquid crystalline polymer as the polymer component of the polymer composition, or may comprise a combination of two or more thermotropic liquid crystalline polymers as the polymer component of the polymer composition. The polymer composition may comprise other non-polymer components, such as additives or reinforcing fibers, electrically or thermally conductive fillers, fillers and additives. Suitable reinforcing fibers are, for example, aramid or inorganic reinforcing fibers, such as glass fibers or carbon fibers. The reinforcing fibers, fillers, and additives may be dispersed in the polymer composition, and may be further oriented in the flow direction of the polymer composition in the solid filamentous units. Suitable conductive fillers are, for example, graphene particles or carbon black. Suitable non-conductive fillers are, for example, titanium dioxide or PTFE. In the context of the present invention, the thermotropic liquid crystalline polymer is not particularly limited. In a preferred embodiment of the additive manufacturing process, the thermotropic liquid crystalline polymer is the only polymer component of the polymer composition that goes into a molten state or a liquid crystalline molten state, and more preferably the thermotropic liquid crystalline polymer is the only polymer component of the polymer composition.

Thermotropic liquid crystalline polymers particularly suitable for use in the present invention are aromatic polyester thermotropic liquid crystalline polymers, such as those obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid.

The thermotropic liquid crystalline polymer is deposited along a predetermined path such that the minimum thickness of one or several filamentary units is equal to or less than 0.2mm, preferably equal to or less than 0.15mm, and more preferably equal to or less than 0.10mm, and most preferably between 0.1mm and 0.01mm. It should be understood that a minimum thickness of the filiform element equal to or less than 0.2mm may be achieved by different strategies. On the one hand, the flow rate of the polymer composition stream through a nozzle having a diameter of less than 0.2mm can be increased, or on the other hand, the flow rate through a nozzle having a diameter of more than 0.2mm can be reduced. Alternatively, the nozzle may be positioned such that the distance between the nozzle orifice and the surface on which the molten matrix of polymer composition is deposited is adjusted to a desired minimum diameter, for example 0.2mm, in which case any filamentary unit formed has at least a minimum diameter in the z-direction, i.e. the minimum diameter of the deposited filamentary unit corresponds to the vertical height of the deposited filamentary unit or the height of the deposited filamentary unit in the z-direction. Generally, the z-direction is orthogonal to the plane of the layer on which the filamentary elements are deposited.

The polymer composition in the molten state is further actively cooled to form solid filamentous subunits, and is preferably actively cooled by forced convection to form solid filamentous subunits. Active cooling may be achieved by, for example, providing an additive manufacturing device with a temperature controlled print accessory. Forced convection may be achieved by means (e.g. fans) capable of directing the flow of coolant fluid towards the deposited filamentary element.

The formed target may then be annealed at a temperature less than 100 deg.C, more preferably less than 50 deg.C, most preferably less than 25 deg.C, below the melting temperature of the thermotropic liquid crystalline polymer for up to 6 hours, preferably up to 9 hours, more preferably up to 12 hours, most preferably up to 48 hours. In the case where the thermotropic liquid crystalline polymer is a polyester obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid, the formed object is preferably annealed at 260 to 280 ℃ for up to 96 hours under a constant nitrogen stream.

The polymer composition discharged from the nozzle of the print head in a molten state may preferably be in a molten liquid crystalline state. In the case where the thermotropic liquid crystalline polymer is a polyester obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid, the temperature at which the molten liquid crystal state exists is 280 ℃ to 320 ℃.

The temperature of the polymer composition discharged from the nozzle of the print head in a molten state may be not more than 100 ℃, preferably not more than 50 ℃, preferably not more than 25 ℃, preferably not more than 15 ℃, and more preferably not more than 5 ℃ higher than the melting temperature of the thermotropic liquid crystalline polymer. In the case where the thermotropic liquid-crystalline polymer is a polyester (for example, a polyester obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid), the temperature of the thermotropic liquid-crystalline polymer discharged in a molten state most preferably corresponds to 285 ℃.

The orifice of the nozzle has a substantially circular orifice and a diameter of less than 0.64mm or 0.05mm to 0.635mm, and preferably a diameter of less than 0.4mm or 0.05mm to 0.4mm, and more preferably a diameter of less than 0.31mm or 0.05mm to 0.305mm, or a substantially rectangular orifice and a diameter of less than 0.64mm or 0.05mm to 0.635mm, and preferably a diameter of less than 0.4mm or 0.05mm to 0.4mm, and more preferably a diameter of less than 0.31mm or 0.05mm to 0.305 mm. In case the minimum diameter of the filamentary subunit is smaller than the diameter of the orifice of the nozzle, the distance between the underlying material and the orifice of the nozzle is adjusted to correspond to the minimum diameter of the filamentary unit.

Examples

FDM filament manufacturing

Liquid crystalline polymers commercially available from Ticona GmbH of germany

A950 (LCP) drying at 150 ℃ for 12 hours before extrusion. Use of a single-screw extruder (` Harbin `)>

E20 T, collin, germany) was prepared LCP filaments which were heated to 280 ℃, 290 ℃ and 260 ℃ at four zones along their longitudinal axis. The filaments were extruded at 60rpm and placed in a water bath (` based `)>

WB850, collin, germany) and collected on the modified flat film production line (` Harbin `)>

CR 72T, collin, germany). The speed of the collector roll was adjusted to achieve a filament diameter of 1.75 mm. The filaments were wound on an FDM roll and dried at 70 ℃ for at least 24 hours prior to use.

FDM print settings

Commercial Fused Deposition Modeling (FDM) printers (Ultimaker 2+, ultimaker, the netherlands) were modified with a geared direct drive extruder and an all metal V6 hot end (E3D, uk) to achieve temperatures up to 400 ℃. A borosilicate glass print bed (built-plate) was heated to 90 ℃ prior to printing with LCP and coated with a thin layer of PVA-based adhesive spray (3 DLac, spain) to improve bed adhesion and reduce warpage. Typically, parts are printed at 295 ℃ at 35 mm/sec with the part cooling fan running at 20%. For the printed line, the speed was reduced to 20 mm/sec to improve the quality of the line in contact with the glass surface.

PLA and PEEK reference samples were printed at temperatures of 210 ℃ and 380 ℃ respectively using commercial Filaments (Dutch fibers b.v., the netherlands and 3D4MAKERS, the netherlands). The print bed was heated to 60 ℃ for PLA and 120 ℃ for PEEK. All other parameters remained the same as for printing the LCP. The PEEK samples were further heat treated at 150 ℃ for one hour and then at 200 ℃ for one hour after printing to achieve optimal crystallization.

A print path (Gcode) with reduced control over the print direction is generated using Cura (open source FDM slicer from Ultimaker). Custom slicers using Grasshopper for Rhinoceros (McNeel, spain) were developed for objects with spatially adjusted directional print paths or those objects for which the orientation of the print path is important.

Thermal annealing

Solid state thermal annealing was performed by heating the sample to 270 ℃ for 0 to 96 hours under a constant nitrogen flow. Solid state crosslinking is believed to occur by post condensation reactions between the carboxylic acid groups of the printed samples. The samples were fixed to a steel plate with polyimide tape to prevent deformation during the annealing process.

Tensile testing of printed filaments (FIG. 1)

Tensile testing was performed on a vertically printed filament starting on the surface (print bed) and moving up (z direction) and horizontally on the glass surface. To produce vertical filaments that do not curl during free-form extrusion, the feedstock material is first printed horizontally to ensure good adhesion to the substrate. Vertical and horizontal filaments were printed at different nozzle diameters and distances from the surface, respectively. In addition, the effects of nozzle temperature and annealing time were examined for both printing configurations.

The filament samples were bonded to individual paper frames according to ASTM C1557 to ensure a constant gauge length of 20 mm. Tensile testing was performed at a rate of 2 mm/min on an AGS-X (Shimadzu, japan) universal tester with a 1kN capacity load cell. The samples were imaged with a light stereo microscope (WILD M10, leica, germany) during the test and the width and thickness of the samples were measured using Fiji image analysis. Data analysis was performed using custom MATLAB scripts.

As can be seen from fig. 1 (a) to 1 (c), the filaments exhibit a core-shell structure. In particular, in (a), this is evidenced by the fact that: the core of the fiber remains intact while the harder outer shell of the liquid crystal polymer filament is broken. Furthermore, the polarized light microscope images in (b) and (c) determine the core-shell structure in the vertical filaments (b) and horizontal (c) filaments, as indicated by the higher illumination of the skins of the printed lines compared to the cores. XRD analysis in (d) further confirmed a higher fraction of oriented domains in the thinner samples. As can be seen from fig. 1 (e), the young's modulus and strength of the vertically extruded filaments increased with decreasing nozzle diameter. The same effect applies to horizontally printed filaments where young's modulus and strength increase with decreasing filament thickness (i.e. height), reaching a maximum modulus of 34GPa and strength of 800MPa at a filament height of 0.05 mm. As can be seen from fig. 1 (g), increased printing temperature results in a decrease in young's modulus. Furthermore, solid state annealing (h) improves mechanical properties by increasing the molecular weight of the polymer and increases filament strength up to 400MPa for vertical extrusion and up to 1GPa for horizontal printing.

Tensile testing of printed parts (FIG. 2)

Tensile testing was performed using a Z020 (Zwick, germany) universal tester with a 20kN capacity load cell. Unidirectional tensile test specimens (ISO 527-5) of nominal width 5mm, length 110mm and thickness 2mm were printed with a printed filament orientation varying from 0 ° to 90 ° relative to the test direction. The samples were supported in the clamping area with bonded fiberglass reinforced polymer end stiffeners to give a gauge length of 65 mm. The samples were tested at a displacement control rate of 2 mm/min. Data analysis was performed using custom MATLAB scripts. In addition to the printing direction, the effect of different layer heights, temperatures and annealing times were also investigated.

As can be seen from fig. 2 (a) and 2 (b), the young's modulus and the flexural modulus of the unidirectional printing member depend on the printing orientation and are highest when the sample is tested in the printing direction (i.e., in the direction of the main orientation of the filaments constituting the sample). In (c) it can be seen that the lower tensile strength in the 90 ° orientation with respect to the printing direction can be improved, in particular by carrying out the annealing for more than 24 hours, due to the improved adhesion between the filaments. As can be seen from fig. 2 (d), for the samples with printed lines oriented in the loading direction, the mode of fracture changed from brookform to ductile laminar fracture due to the improved filament adhesion achieved by thermal annealing (96 hours). This change also results in a jagged fracture pattern in the stress-strain curve, which increases the amount of energy (modulus of toughness) required to fracture the part by a factor of 2.

The tensile test may also be performed on the FDM printing target by: tensile specimens were cut from a region of the object in dimensions according to ISO 527 and ASTM D638 for polymers, according to ISO 527 and ASTM D3039 for composites, and according to ASTM C1273 and ISO 15490 for ceramics, and tested in a tensile tester according to the above listed standards to measure young's modulus and tensile strength.

Bend testing of printed parts

The bending test was performed on an AGS-X (Shimadzu, japan) universal testing machine with a three-point bending setting using a span of 24 mm. Samples with different thicknesses (layer heights) were measured before and after annealing at a displacement control rate of 2 mm/min. Specimen geometry and bending test setup were selected according to ISO 14125. A span to thickness ratio of 16 was used to ensure a bending stress state and limited effect of constant shear stress within the specimen.

List of reference numerals

Is free of

Claims

1. An additive manufacturing method for manufacturing an object in an additive manufacturing apparatus, wherein the object is formed by one or several individual solid filamentary units, the additive manufacturing method comprising the steps of:

-extruding a polymer composition in the molten liquid crystalline state from an extrusion nozzle of a print head, thereby imparting an oriented flow to the polymer composition in the molten state discharged from the nozzle of the print head and depositing the polymer composition in the molten state discharged along at least one predetermined path and solidifying the threadlike unit or units thus formed to form a solid threadlike unit or units of the object to be manufactured;

-optionally repeating the previous step until said target is formed;

wherein the polymer composition consists of only a thermotropic liquid crystalline polymer as a polymer component of the polymer composition or only a thermotropic liquid crystalline polymer as a polymer component of the polymer composition and additives, characterized in that the minimum thickness of the one or several solid threadlike units is less than 0.15mm, and wherein the one or several solid threadlike units consist of only a thermotropic liquid crystalline polymer or only a thermotropic liquid crystalline polymer and additives.

2. The additive manufacturing method of claim 1, wherein the path is a horizontal path.

3. The additive manufacturing method according to claim 1, wherein the minimum thickness of the one or several filamentary units is less than 0.10mm.

4. The additive manufacturing method according to claim 1, wherein the minimum thickness of the one or several thread-like units is 0.1mm to 0.01mm.

5. The additive manufacturing method according to claim 1, wherein the polymer composition in the molten state is further actively cooled to form a solid filamentous unit.

6. The additive manufacturing method according to claim 1, wherein the polymer composition in the molten state is actively cooled by forced convection to form a solid filamentous unit.

7. The additive manufacturing method according to any one of claims 1 to 6, wherein the formed target is subsequently annealed at less than 100 ℃ below the melting temperature of the thermotropic liquid crystalline polymer for up to 48 hours.

8. The additive manufacturing method according to claim 7, wherein the formed object is annealed at less than 50 ℃ below the melting temperature of the thermotropic liquid crystalline polymer.

9. The additive manufacturing method according to claim 7, wherein the formed target is annealed less than 25 ℃ below the melting temperature of the thermotropic liquid crystalline polymer.

10. The additive manufacturing method of claim 7, wherein the formed target is annealed for up to 9 hours.

11. The additive manufacturing method of claim 7, wherein the formed target is annealed for up to 12 hours.

12. The additive manufacturing method of claim 7, wherein the formed target is annealed for up to 6 hours.

13. The additive manufacturing method according to any one of claims 1 to 6, wherein the polymer composition in the melt crystalline state is ejected from a nozzle of the print head along a non-linear path.

14. The additive manufacturing method according to any one of claims 1 to 6, wherein the thermotropic liquid crystalline polymer is an aromatic polyester.

15. The additive manufacturing method according to claim 14, wherein the thermotropic liquid crystalline polymer is a polyester obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid.

16. The additive manufacturing method of any one of claims 1 to 6, wherein a temperature of the polymer composition discharged from a nozzle of a print head in a molten state is no greater than 50 ℃ higher than a melting temperature of the thermotropic liquid crystalline polymer.

17. The additive manufacturing method of claim 16, wherein the temperature of the polymer composition discharged from a nozzle of a print head in a molten state is no greater than 25 ℃ above the melting temperature of the thermotropic liquid crystalline polymer.

18. The additive manufacturing method of claim 16, wherein the temperature of the polymer composition discharged from a nozzle of a print head in a molten state is no greater than 15 ℃ above the melting temperature of a thermotropic liquid crystalline polymer.

19. The additive manufacturing method of claim 16, wherein a temperature of the polymer composition discharged from a nozzle of a print head in a molten state is no greater than 5 ℃ above a melting temperature of a thermotropic liquid crystalline polymer.

20. The additive manufacturing method according to any one of claims 1 to 6, wherein the orifice of the nozzle has a substantially circular orifice and a diameter of less than 0.64mm or 0.05mm to 0.635mm, or a substantially rectangular orifice and a diameter of less than 0.64mm or 0.05 μm to 0.635 μm.

21. The additive manufacturing method of claim 20, wherein the orifice of the nozzle has a substantially circular orifice and a diameter of less than 0.4mm or 0.05mm to 0.4 mm.

22. The additive manufacturing method of claim 20, wherein the orifice of the nozzle has a substantially circular orifice and a diameter of less than 0.31mm or 0.05mm to 0.305 mm.

23. The additive manufacturing method of claim 20, wherein the orifice of the nozzle has a substantially rectangular orifice and a diameter of less than 0.4mm or 0.05mm to 0.4 mm.

24. The additive manufacturing method of claim 20, wherein the orifice of the nozzle has a substantially rectangular orifice and a diameter of less than 0.31mm or 0.05mm to 0.305 mm.

25. An object obtained by the additive manufacturing method according to any one of the preceding claims, wherein the young's modulus of a region of the object is 15GPa or more, and/or wherein the tensile strength of a region of the object is 200MPa or more, wherein the object consists of a polymer composition consisting of only a thermotropic liquid crystalline polymer, or only a thermotropic liquid crystalline polymer as a polymer component of the polymer composition, and additives.

26. The object of claim 25, wherein the region of the object has a young's modulus of 20GPa or higher and up to 25GPa.

27. The object of claim 25, wherein the region of the object has a tensile strength of 200MPa and up to 500MPa.

28. The object of claim 25, wherein the region of the object has a tensile strength of 300MPa and up to 500MPa.

29. The object according to claim 25, wherein the object comprises or consists of at least one solid filamentous subunit having a minimum thickness equal to or less than 0.2mm.

30. The object according to claim 29, wherein the minimum thickness of the at least one solid filamentous subunit is equal to or less than 0.15mm.

31. The object according to claim 29, wherein the minimum thickness of the at least one solid filamentous subunit is equal to or less than 0.10mm.

32. The object according to claim 29, wherein the minimum thickness of the at least one solid filamentous subunit is from 0.01mm to 0.10mm.

33. The object according to any one of claims 25 to 32, wherein the polymer composition comprises a thermotropic liquid crystalline polymer as the sole polymer component of the polymer composition material, wherein the young's modulus of a region of the object is 15GPa or more and/or wherein the tensile strength of a region of the object is 200MPa or more.

34. The object according to claim 33, wherein the region of the object has a young's modulus of 20GPa or higher.

35. The target of claim 33, wherein the region of the target has a young's modulus of 25GPa or greater.

36. The target of claim 33, wherein the region of the target has a young's modulus of 25GPa to 35GPa.

37. The object of claim 33, wherein the region of the object has a tensile strength of 400MPa or greater.

38. The object of claim 33, wherein the region of the object has a tensile strength of 600MPa or greater.

39. The object of claim 33, wherein the region of the object has a tensile strength of 600MPa to 1GPa.

40. An additive manufacturing apparatus comprising at least one supply of a polymer composition and configured to perform the additive manufacturing method according to claims 1 to 24, characterized in that the polymer composition consists only of thermotropic liquid crystalline polymer as a polymer component of the polymer composition or only of thermotropic liquid crystalline polymer as a polymer component of the polymer composition and an additive.

41. The additive manufacturing apparatus according to claim 40, wherein the thermotropic liquid crystalline polymer that is a polymer of the polymer composition is obtained by polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid.

42. Additive manufacturing apparatus according to claim 40 or 41, further comprising a build envelope equipped with a heating device capable of maintaining the target in a build space at a temperature corresponding to an annealing temperature of the thermotropic liquid crystalline polymer.